Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $119.33   7.607%   $128.4074   $128.41   $128.40   $128.40  
  Purchase #2 $231.79   8.113%   $250.5951   $250.60   $250.60   $250.60  
  Purchase #3 $14.98   11.522%   $16.706   $16.71   $16.70   $16.70  
  Purchase #4 $227.44   11.542%   $253.6911   $253.69   $253.70   $253.70  
  Purchase #5 $125.28   3.399%   $129.5383   $129.54   $129.55   $129.50  
  Purchase #6 $32.66   11.222%   $36.3251   $36.33   $36.35   $36.30  
  Purchase #7 $53.46   10.451%   $59.0471   $59.05   $59.05   $59.00  
  7 purchase totals = $804.94       $874.3101   $874.33   $874.35   $874.20